Lens system having a long focal length

ABSTRACT

A lens system having a long focal length, which consists of a first positive lens component, a second positive meniscus lens component that has at its object side a convex surface, a third negative lens component, a fourth negative lens component and a fifth positive lens component, large air spaces being present between the third component lens and the fourth component lens and between the fourth lens components and the fifth lens components, respectively, and which is defined by the following five conditions, i.e., 1. 0.7F &gt; F1,2,3 &gt; 0.4F, 2. 0.05F &gt; D2 &gt; 0.01F, 3. R5 &gt; 3F, R5 &gt; 0, 4. 0.2F &gt; D8 &gt; D6 &gt; 0.1F, AND 5. F &gt; F5 &gt; 0.8F WHERE F IS A COMPOSITE FOCAL LENGTH OF THE TOTAL LENS SYSTEM, F1,2,3 IS A COMPOSITE FOCAL LENGTH OF THE FIRST, SECOND AND THIRD COMPONENT LENSES, AND RI (I 1, 2, . . . 10) AND DI (I 1, 2, . . . 9) ARE RADII OF CURVATURES OF THE SUCCESSIVE LENS SURFACES COUNTED FROM THE SIDE OF AN OBJECT AND AXIAL THICKNESSES OF OR AIR SPACES BETWEEN THE SUCCESSIVE LENSES COUNTED FROM THE SIDE OF THE OBJECT, RESPECTIVELY. The telephoto ratio is on the order of 0.85 - 0.9.

uulwu mat Nakagawa 1 LENS SYSTEM HAVING A LONG FOCAL LENGTH [75]lnventor:

Jihei Nakagawa, Tokyo, Japan Assignee: Olympus Optical Company Limited,

Tokyo, Japan Filed: Apr. 7, 1972 Appl. No.: 241,926

[30] Foreign Application Priority Data- Apr. 9, l97l Japan 46/2l789 US.Cl. 350/2l8, 350/176 Int. Cl. G02b 9/60, G02b 13/02 Field of Search350/2l8, 176, 215

[56] References Cited UNITED STATES PATENTS l0/l942 Warmisham 350/2l8 X9/1969 Kazamaki et al. 350/l77 X Primary Examiner.lohn K. CorbinAn0rneyEric H. Waters et al.

[57] ABSTRACT A lens system having a long focal length, which consists LLZLJ L4 [451 Sept. 25, 1973 where f is a composite focal length of thetotal lens systern, f 3 is a composite focal length of the first, secondand third component lenses, and r,- (i=1, 2, l0) and d, (i=1, 2, 9) areradii of curvatures of the successive lens surfaces counted from theside of an object and axial thicknesses of or air spaces between thesuccessive lenses counted from the side of the object. respectively. Thetelephoto ratio is on the order of 0.85 0.9.

3 Claims, 7 Drawing Figures r, as? t d d? {U} 6' UM, d2

PAIENIED 25 75 SHEET 1 0f 2 FIG./

FIG. 2a F/azu P161126 PAliNIEnstrzsma SHEHZBFZ F [6.30 FIG. 3b F/6 3 mmmm 1 LENS SYSTEM HAVING A LONG FOCAL LENGTH This invention relates to alens system having a long focal length, which has been known as Ernostartype lens system having a long focal length.

The Ernostar type lens system having a long focal length hassignificantly corrected spherical aberration, astigmatism, distortion,etc., but has the disadvantage that the telephoto ratio (the ratio ofthe distance between the front surface of the first lens component andthe film surface to the composite focal length of the whole lens system)could not be made small.

The object of the invention, by increasing the refractive power of thefirst and second lenses of the Ernostar type lens system and by adding anegative lens to the rear side of the second lens so as to correct theaberration which is produced by the increased refractive power of thefirst and second lenses, and by adopting suitable air spaces betweeneach lens component and adjacent component lenses, is to provide a lenssystem having a long focal length, whose telephoto ratio is extremelysmall, on the order of 0.85 0.9, and which has significantly correctedspherical aberration, astigmatism, distortion, etc.

A feature of the invention is the provision of a lens system having along focal length, which consists of a first positive lens component, asecond positive meniscus lens component that has at its object side aconvex surface, a third negative lens component, a fourth group ofnegative lens component, and a fifth positive lens component, large airspaces being present between the third lens component and the fourthlens component and between the fourth lens component and the fifth lenscomponent, respectively, and which is defined by the following fiveconditions, i.e.

2. 0.05f d 0.0lf,

4. 0.2f d a O.lf, and

5. f f, 0.8f wherefis a composite focal length of the total lenssystem,f,, is a composite focal length of the first, second and thirdlens components, and r, (i=1, 2, l) and i d,- (i=1, 2, 9) are radii ofcurvatures of the successive lens surfaces counted from the side of anobject and axial thicknesses of or air spaces between the successivelenses counted from the side of the object, respectively.

For a better understanding of the invention, the same will be explainedby reference to the accompanying drawings, in which:

FIG. 1 shows in cross-section a lens system having a long focal lengthconstructed according to the invention;

FIGS. 20 to 2c show aberration characteristic curves of one embodimentof the invention; and

FIGS. 3a to 3c show aberration characteristic curves of anotherembodiment of the invention.

Referring to the drawings, a lens system having a long focal distanceaccording to the invention is shown in FIG. I in which L, designates afirst positive lens component, L shows a second positive meniscus lenscomponent that has at its object side a convex surface, L illustrates athird negative lens component, L designates a negative lens component,and L shows a fifth positive lens component.

In accordance with the invention a large air space d is present betweenthe third lens component L and the fourth lens component L. A large airspace d is also present between the fourth lens component L and thefifth lens component L Moreover, the composite focal length f of thefirst, second and third lens components L L and L;,, the air space d;between the first lens component L, and the second lens component L theradius of curvature r of the front surface of the third lens componentL;,, the air space d., between the third and fourth lens component L andL,, the air space d between the fourth and fifth lens components L, andL and the focal length j}, of the fifth lens component L are defined bythe following five conditions, respectively, i.e.

2. 0.05f d 0.0lf.

5. f f 0.8f where f is a composite focal length of the total lenssystem, f is composite focal length of the first, second and third lenscomponents L L and L and r, (i=1, 2,... l0) and d, (i=1, 2, 9) are radiiofcurvatures of the successive lens surfaces counted from the side of anobject and axial thicknesses of or air spaces between the successivelenses counted from the side of the object, respectively.

The above mentioned condition l relates to the telephoto ratio. If f, isnot less than 0.7f and is not larger than 0.4 f, it is impossible toobtain a lens system having a long focal distance and havingsignificantly corrected spherical aberration, astigmatism, distortion,etc. and whose telephoto ratio is extremely small, on the order of 0.850.9. lff is smaller than 0.4f, the refractive power of the fourth lenscomponent L, becomes strong. This, however, is not desirable for thecorrection of aberrations. lff is larger than 0.7f, it is impossible tomake the telephoto ratio on the order of 0.85 0.9.

In the condition (2), ifd becomes smaller than 0.0 lf, the coma on theperiphery of the picture surface can be improved. This, however, resultsin a difficulty in removing the chromatic aberrations on axis and onmagnification. On the contrary, if d is larger than 0.051", thechromatic aberration can be corrected, while the coma, and moreparticularly, the coma on the periphery of the picture surface becomesdegraded.

The condition (3) is essential for the correction of the sphericalaberration, chromatic aberration on axis, coma and astigmatism. If I ris smaller than 3f, it is difficult to correct the spherical aberrationand the chromatic aberration on axis. If r 0, the coma and astigmatismbecome degraded. It is difficult to significantly correct the coma andastigmatism even though the other elements are changed.

The condition (4) is associated with the conditions l and (5). lfd issmaller than 0. 1 f, it is impossible to make the telephoto ratio smallon the order of 0.85 0.9. If d becomes smaller than d,;, it isimpossible to significantly correct the distortion. lf d is larger than0.2f, the improvement of the symmetry of the aberration out of axisbecomes difficult.

In the condition (5 if f is smaller than 0.8f, the bobbin typedistortion can be made small, but the coma becomes degraded. lff, islarger than f, the distortion is increased.

The invention will now be described with reference to the followingexamples.

The telephoto ratio=0.87

The aberration characteristic curves of the present embodiment are shownin FIGS. 2a to 2c. FIG. 2a shows the spherical aberrations and sineconditions, F 16. 2b the astigmatisms, and FIG. 2c the distortion.

As seen from these aberration characteristic curves, the lens systemaccording to the present embodiment makes it possible to significantlycorrect these aberrations. Particularly, the above Table shows that thetelephoto ratio is 0.87.

The telephoto ratio=0.9

positive meniscus lens component that has at its object side a convexsurface, a third negative lens component. a fourth negative lenscomponent, and a fifth positive lens component. large air spaces beingpresent between the third lens component and the fourth lens componentand between the fourth lens component and the fifth lens component,respectively, and which is defined by the following five conditions,i.e.,

4. 0.2f d a 0.1f, and

5. f f 0.8f where f is a composite focal length of the total lenssystern, f is a composite focal length of the first, second and thirdlens components, and r, (i=1, 2, l0) and d, (=1, 2, 9) are radii ofcurvatures of the successive lens surfaces counted from the side of anobject and axial thicknesses of or air spaces between the successivelenses counted from the side of the object, respectively.

2. A lens system having a long focal length as claimed in claim 1,whereinF1.0,fl, =0.52l, 1:3.5,f =0.857 and the telephoto ratio is 0.87and r, to r d to (1,, n to n and u, to u are defined by the followingvalues 3. A lens system having a long focal length as claimed in claim1, wherein F1.O,f,, =0.559, 1:2.8,f =0.869 and the telephoto ratio is0.9 and r, to 4, d to d n to n and v, to u are defined by the followingvalues

1. A lens system having a long focal length, which consists of a firstpositive lens component, a second positive meniscus lens component thathas at its object side a convex surface, a third negative lenscomponent, a fourth negative lens component, and a fifth positive lenscomponent, large air spaces being present between the third lenscomponent and the fourth lens component and between the fourth lenscomponent and the fifth lens component, respectively, and which isdefined by the following five conditions, i.e.,
 1. 0.7f > f1,2,3 > 0.4f,2. 0.05f > d2 >0.01f,
 3. r5 > 3f, r5 < 0,
 4. 0.2f > d8 > d6 > 0.1f, and5. f > f5 > 0.8f where f is a composite focal length of the total lenssystem, f1,2,3 is a composite focal length of the first, second andthird lens components, and ri (i 1, 2, . . . 10) and di ( 1, 2, . . . 9)are radii of curvatures of the successive lens surfaces counted from theside of an object and axial thicknesses of or air spaces between thesuccessive lenses counted from the side of the object, respectively. 2.A lens system having a long focal length as claimed in claim 1, whereinf 1.0, f1,2,3 0.521, 1:3.5, f5 0.857 and the telephoto ratio is 0.87 andr1 to r10, d1 to d9, n1 to n11 and Nu 1 to Nu 5 are defined by thefollowing values n1 1r1 0.3644d1 0.0456n2 1.618 Nu 1 63.38r2 -3.2138d20.0196n3 1r3 0.3799d3 0.0397n4 1.618 Nu 2 63.38r4 1.1428d4 0.0119n5 1r5-4.2528d5 0.0172n6 1.76182 Nu 3 26.55r6 0.6858d6 0.1271n7 1r7 1.9622d70.0171n8 1.66998 Nu 4 39.32r8 0.2119d8 0.1508n9 1r9 1.1395d9 0.0138n101.80518 Nu 5 25.43r10 -1.7395n11 1
 2. 0.05f > d2 >0.01f,
 3. r5 > 3f, r5< 0,
 3. A lens system having a long focal length as claimed in claim 1,wherein f 1.0, f1,2,3 0.559, 1:2.8, f5 0.869 and the telephoto ratio is0.9 and r1 to 410, d1 to d9, n1 to n11 and Nu 1 to Nu 5 are defined bythe following values n1 1r1 0.4104d1 0.0579n2 1.618 Nu 1 63.38r2-3.6443d2 0.0297n3 1r3 0.3853d3 0.0505n4 1.618 Nu 2 63.38r4 1.4567d40.0125n5 1r5 -4.1705D5 0.0201n6 1.761823 26.55r6 0.6713d6 0.1154n7 1r71.5982d7 0.0216n8 1.66998 Nu 4 39.32r8 0.2255d8 0.1515n9 1r9 11.8177d90.0250n10 1.80518 Nu 5 25.43r10 -0.7426n11 1
 4. 0.2f > d8 > d6 > 0.1f,and
 5. f > f5 > 0.8f where f is a composite focal length of the totallens system, f1,2,3 is a composite focal length of the first, second andthird lens components, and ri (i 1, 2, . . . 10) and di ( 1, 2, . . . 9)are radii of curvatures of the successive lens surfaces counted from theside of an object and axial thicknesses of or air spaces between thesuccessive lenses counted from the side of the object, respectively.